1. Field of the Invention
The present invention is related to a method and apparatus for surface diagnostics of substrates, in particular substrates used in the production of integrated circuit devices.
2. Description of the Related Technology
The known techniques for mass spectrometry include the Secondary Ion Mass Spectrometry (SIMS) method. This method uses an ion beam directed at a sample under investigation, which sputters a quantity of neutral and ionized matter from the sample""s surface. The ions that are formed are then accelerated towards a mass spectrometry device.
Like many other techniques, SIMS is a method which disrupts the atomic structure of the sample. This makes it unadapted for the so-called xe2x80x98depth-profilingxe2x80x99, which is a measurement of the sample""s composition as a function of depth. Accurate depth profiling is performed xe2x80x98layer by layerxe2x80x99, the thickness of each layer being as close as possible to the dimensions of one atom (near atomic accuracy). The important thing is to be able to free atoms in the layer closest to the surface, without disrupting atoms lying underneath the top layer. Current methods are not capable of performing depth profiling on a near atomic level of accuracy.
U.S. Pat. No. 4,733,073 describes a method and apparatus wherein a probe beam, such as an ion beam, an electron beam or a laser beam is directed at the sample under high vacuum. In a region close to the impact of the probe beam, the sputtered samples are ionized by non-resonant photoionization which allows a non-selective analysis of species present in the sample. This document speaks of regulating the probe beam""s intensity in order to perform depth-profiling. Other methods have been described such as the Floating LowEnergy Ion Gun technique (FLIG(copyright)), described in the document xe2x80x98An ultra-low energy ion column for sputter profilingxe2x80x99 by M. G. Dowsett et al., proceedings of the Tenth International Conference on Secondary Ion Mass Spectrometry (SIMS X), Munster, Germany, Oct. 1-6, 1995. This last method has the objective to reduce the probe beam""s energy down to 200 eV, in order to perform depth profiling. However, even at low energy level, the disruption of the atomic structure remains a problem when using ion beam technology.
The use of a laser as the probe beam, such as mentioned in U.S. Pat. No. 4,733,073 has the effect of ablation, i.e., wearing away parts of a sample by heating and subsequent evaporation or sublimation of the sample. This reaction can never be controlled so that it will only affect a top layer of atoms. A laser is therefore not suited for an accurate depth profiling.
Low energy electron beams are incapable of producing sufficient energy to release atoms from a sample. Increasing their energy will cause heat effects similar to the ones caused by laser beams.
Besides accurate depth profiling, higher demands are presently made in terms of the size of the analysed area on the sample surface, meaning that ever smaller areas, in particular areas of less than 1 xcexcm2 are becoming currently accessible. The current way of handling this problem is using ion beam technology by reducing the ion beam diameter, which invariably necessitates increasing the beam energy. This led to the development of high energy beams, such as used in the known Focused Ion Beam (FIB(copyright)) technique, described in xe2x80x98The integration of a high performance quadrupole SIMS facility with a Ga+ LMIS based FIB Instrumentxe2x80x99, T. Dingle et al., proceedings of the Tenth International Conference on Secondary Ion Mass Spectrometry (SIMS X), Mxc3xcnster, Germany, Oct. 1-6, 1995. It is clear that this increased beam energy is detrimental to the preservation of atomic structures, as required for accurate depth profiling.
One aspect of the invention provides a method which allows accurate analysis of the composition of a sample, including depth profiling at near atomic level.
Another aspect of the invention provides a method which, in combination with the depth profiling, allows the analysis of areas smaller than 1 xcexcm2.
Another aspect of the invention is related to a method for performing a surface analysis of a sample. The method comprises placing a sample having a surface in an enclosure in which a low pressure is present, providing a gas mixture in close proximity with the surface, the mixture comprising one or more reactive gases, and applying a probe beam on a location of the surface so as to create an etching on the location. The method also comprises ionizing an etching product which is originated from the location of the surface so as to generate at least one ion, accelerating the at least one ion towards a mass spectrometer, and performing a mass spectrometry analysis on the at least one ion in the mass spectrometer.
Still another aspect of the invention provides an apparatus for performing a surface analysis of a sample. The apparatus comprises an enclosure, a gas mixture introducing portion, a maintaining portion, a probe beam provider, a laser beam provider, an accelerating portion and a mass spectrometer. The enclosure contains a sample having a surface. The gas mixture introducing portion introduces a gas mixture into the enclosure. The maintaining portion maintains the gas mixture in a predefined condition at close proximity to the surface. The probe beam provider provides a probe beam at a predefined location on the surface of the sample so as to create an etching on the location. The laser beam provider provides at least one laser beam to an etching product released from the location so as to produce at least one ion. The accelerating portion accelerates the at least one ion. The mass spectrometer performs a mass spectrometry on the accelerated at least one ion.
Yet another aspect of the invention provides a method of performing a surface analysis of a sample. The method comprises providing a gas mixture near a surface of the sample, the mixture comprising one or more reactive gases and applying a probe beam on a location of the surface such that the interaction between the probe beam, the gas mixture and the sample surface takes place and results in a compound being released from the surface. The method comprises ionizing the compound so as to generate at least one ion and performing a mass spectrometry analysis on the at least one ion.